1. Field of the Invention
This invention relates to a table mechanism requiring precise control of position for use in ultraprecision machine tools, manufacturing machines for semiconductors or the like, etc., especially in surface finish grinding of semiconductor wafer substrates, grinding of magnetic heads and machining of lenses.
2. Description of the Related Art
In general, table mechanisms moving straight are available in the following types:
(1) a feed screw type in which a feed screw attached rotatably in its axial direction to the supports is turned to move the table through the nuts attached to the table.
(2) a rack and pinion type in which a pinion provided on the support is engaged with a rack mounted on the table side and is driven to move the table.
(3) a wire type in which a wire connected to the support is tightened up to move the table which has slided along the support.
In the feed screw (regular screw of ball screw) mechanism of (1), an error in mounting the table guideway and the feed screw, a deflection caused by the weight of the screw, or a disturbance exerted by twisting motion of the screw will affect the table through the nuts. Especially in the case of the workpiece formed of a hard brittle material such as the aforementioned semiconductor wafers, magnetic heads or lenses, if vibration occurs to the workpiece, fine vibration, for example, may cause chipping and affect machining accuracy. On the other hand, in the rack and pinion system of (2), since the engagement of the rack and pinion produces forces perpendicular to the table movement direction, the machining acuracy is adversely affected. Unlike the above-mentioned two systems, in the wire system of (3), no disturbance occurs, but the wire is apt to elongage, thereby deteriorating the rigidity in the driving system.